The methods known for making dense ceramic parts involve shaping a body of ceramic particles and firing the body to sinter the particles. While various methods such as extrusion, injection molding, etc. have been developed in recent years, "dry pressing" still remains as a widely used method of molding green ceramic parts. Processes falling in the category of dry pressing include cold pressing and isostatic pressing. These processes are characterized by the molding of a free flowing ceramic powder/binder mixture.
Dry pressing is advantageous in that it uses a low amount of binder compared to many of the other molding processes. Nevertheless, processes used in the past have often involved the use of organic solvents in the course of mixing the ceramic particles and the binder. Further, the low level of binder leads to various concerns regarding performance in the dry pressing process.
In dry pressing, there is a concern regarding the formability of the powder into a desired shape. A powder system having good formability makes it easier to mold the desired part without need for extremely high pressing pressures. High molding pressure is generally undesirable since it can lead to stress concentration and crack formation in the green body and fired part. The molded part should also have sufficient green strength and good die release characteristics (i.e. no sticking) so the pressed part can be removed from the die without breakage or creation of defects. Defects in the green ceramic body are usually retained in the sintered ceramic part.
Another source of defects in the dry pressing process can occur when the powder particle agglomerates retain rigidity during pressing. Efficient packing may not occur during the pressing in those circumstances. This poor packing can result in voids or relic structures during binder removal and sintering.
While there are many known binder systems used in dry pressing applications, most involve the use of organic solvents which present an environmental problem. Thus, there is a need for new binder systems to meet performance demands while eliminating the need to use organic solvents.